The present invention relates to systems to determine a geometry parameter of an unknown object.
Attention is called to U.S. Letters Patent of the Inventor B. Shawn Buckley herein: U.S. Pat. Nos. 4,095,475; 4,200,921; and 4,287,769.
In manufacturing, the majority of parts produced are done by a process called batch manufacturing. Batches of parts from 50 to perhaps 1000 are processed at one time. Batch processing which represents 75% of the dollar value of all parts manufacturing, is economically appropriate for those parts which are made in volumes of less than a million parts per year. However, batch processing is a labor intensive method which necessarily means the cost per unit is relatively high compared to automated parts manufacturing or, "hard automation".
In hard automation, part volumes are high enough that a machine can be specially built and dedicated to the manufacture of a particular part. Usually a million or more parts per year are needed to economically justify such a dedicated machine. It is called hard automation because "hard" tooling is needed to manufacture a particular part. If the design of a part should change, often another machine must be built to automate its manufacture even for relatively minor changes in the design. Despite the drawback of requiring special-purpose machines for each part design, hard automation remains the most economical method of manufacturing when millions of a part are to be made.
"Soft" automation is an attempt to apply hard automation principles to batch processing: it replaces the "hard" tooling with electronic computers. The computers can be quickly reprogrammed to manufacture a part of a different design without performing the task manually or redesigning the machine that makes the part. In metal cutting, "soft" automation incorporates numerically controlled (NC) lathes and milling machines. In warehousing, it incorporates automated retrieval systems. In paint spraying and spot welding, it incorporates industrial robots. On the factory floor it incorporates programmable controllers.
However, in parts handling and assembly systems the versatility of "soft" automation has not been realized. True, industrial robots can be programmed to manipulate a part in enormously complicated ways once given a part to manipulate. But unfortunately, it has no versatile way of obtaining the parts in the first place. Each robot comes equipped with custom-tooled parts feeders-whose cost is typically three to five times the cost of the robot itself. These parts feeders, the dominant cost in a robot parts handling system, must be custom designed and installed for each part a robot manipulates. Thus the robot becomes a mere accessory to what is essentially a hard automation system. While the robot may be versatile enough to handle a variety of parts, the systems to which it is coupled are not.
Vision systems are an attempt by "soft" automation experts to couple the robot to the parts that it must handle. Unfortunately, these systems are expensive compared to manual methods. Although they hold the promise of enabling a robot to feed its own parts, presently they are not a practical method of doing so. A versatile, low-cost method of allowing a robot to grasp parts which it manipulates is required.
Acoustic systems exist which determine some information about objects which a robot is to grasp. These systems use either "pulsed" methods or "continuous wave frequency modulated" (CWFM) methods. The pulsed methods send out a "pulse" of sound followed by a silent period during which a receiver listens for the reflected sound pulse from the object. By measuring the delay time between send and receive, the distance to an object can be measured. An acoustic range-finder camera made by Polaroid Corporation of Cambridge, Mass., uses such a principle to determine the distance between the camera and nearby objects for focusing purposes. While such devices can detect an object's proximity, its shape cannot be determined without scanning an object (physically moving the sound source to points at various parts of the object). Moreover, reflections from jigs and fixtures, common in industrial parts handling, can be detected rather than the reflections from the object. It will be noted that most pulsed acoustics (e.g., the acoustic tomography associated with medical ultrasound applications) inherently uses a liquid medium which is not appropriate for robots grasping objects in an industrial setting.
CWFM is a technique using continuous acoustic waves whose frequency varies over a broad range. The sound waves are transmitted toward an object and reflections received by appropriate transducers. The reflected signals are electronically mixed with the transmitted signal and then translated into the frequency domain, usually by an FFT (fast Fourier transform) algorithm. In this procedure, objects close to the transducers give a response at low frequency while objects further from the transducers give a high frequency response. Acoustic CWFM in air has been developed primarily in New Zealand where it is used as an aid for the blind (D. Rowell "Auditory Display of Spatial Information", PH.D. Thesis, University of Caterbury, Christchurch, New Zealand, 1970). It holds promise as a method by which a robot can grasp an object. Indeed, bats use such a technique for locating flying insects in total darkness.
The present invention uses continuous wave (CW) at a single frequency as opposed to the pulsed technique or the variable frequency continuous wave technique. By operating at a single frequency, digital and analog filtering techniques can be employed which give higher accuracy measurements than the other acoustic techniques. Moreover, transducers which operate at a single frequency are easier to construct than broad band transducers which must operate over large frequency bands, as in CWFM, and, in some cases, in pulsed acoustics.
The present invention can be used for imaging an object in an unstructured environment. "Unstructured", in this case means that the environment is not known ahead of time. By contrast, the previous applications of CW acoustics, discussed in the Buckley U.S. Pat. Nos. 4,095,475; 4,200,921 and 4,287,769, were in the context of "structured" environments where objects were previously known and only small variations of those objects were measured. The present invention is a method by which an array of acoustic transducers is implemented in automated manufacturing systems using industrial robots and the like, where at least some parts of the object or environment are not known beforehand.
The issue of "structured" and "unstructured" environments is a vague one and can best be explained in relation to how far an object is from its "expected" position, or how far it has changed from its "expected" shape. Since the position, orientation and shape of an object all affect the acoustic measurements in a similar way, henceforth only position will be referred to, but with the understanding that shape and orientation (also called geometry parameters or characteristics herein) changes are included. A "structured" environment, in this context, means that all objects are close to their expected position: an "unstructured" environment is one where objects might be at any position, previously unknown. In the Buckley patents, wave measurements are compared to previous measurements of a standard or reference object. Hence, the environment is structured because only variations in the position of the standard object are measured.